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This is a good recommendation, as long you got a long piece of wood flat enough and put the phone on it.
@JWestland as you know already, every bike is different, but when it come to setting up another bike, it's always vital to get the saddle - BB distance sorted first, then sort out the angle.
Then you can finish it off with the cockpit and the like.
P.S. handlebar height can make a difference to how a saddle at the same angle feel.
Or just use a spirit level app on your phone, that's what I did to set mine up, worked fine.